Relations among heterotrophic bacteria, chlorophyll-a, total phytoplankton, total zooplankton and physical and chemical features in the Paranoa reservoir, Brasilia, Brazil

The plankton community, chlorophyll-a, heterotrophic bacteria and physical and chemical features of the Paranoa Reservoir were studied at monthly intervals at seven stations from March 1988 to March 1989. Thermal structure had a circulation period from May to July and stratification during the other months. The phytoplankton consisted of 76 taxa, was dominated by the cyanophyte Cylindrospermopsis raciborskii and attained concentrations ranging from 7,759,000 up to 98,160,000 org. l(-1). The zooplankton consisted of 36 taxa and was present in densities between 8 and 8,056 org. l(-1). In stations, or seasons with highly eutrophic conditions, there was a decrease in total phytoplankton and an increase in bacteria and total zooplankton. The results had spatial and temporal variations. Spatial variation demonstrated the existence of water quality deterioration at two or three sampling points. Temporal variation showed the influences of water column stability and the dry versus rainy seasons on nutrient concentrations and the planktonic community.